What is XPS or OXPS?
XPS stands for for XML Paper Specification.
OXPS stands for for Open XML Paper Specification.
XPS or OXPS is used as the file extension for Open XML Paper Specification files.
.XPS or .OXPS files are binary files that can be opened by Microsoft XPS Viewer or orther XPS software.
See the sample .XPS file included below.

✍: FYIcenter.com

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File Extension: .XPS or .OXPS

MIME Type: application/oxps

File Content: Open XML Paper Specification

.XPS or .OXPS files are Open XML Paper Specification files saved as binary files.
An .XPS or .OXPS file is actually a ZIP archive using the Open Packaging Conventions,
containing the files which make up the document.
These include an XML markup file for each page, text, embedded fonts, raster images,
2D vector graphics, as well as the digital rights management information.

The contents of an .XPS or .OXPS file can be extracted by any ZIP tools.
See the ZIP file identifier "PK" in the first 64 bytes of a sample .XPS file dumped in HEX values: